In recent years, various mobile communication media become popular rapidly. In such mobile communication media, there are included automobile telephone, portable telephone, and pager (small-sized radio paging receiver). Among them, small-sized radio paging receivers are spreading widely because each of the radio receivers is small sized as a whole and the price is low.
Heretofore, as such a small-sized radio paging receiver (small-sized communication device), a wristwatch-type radio paging receiver having a coil antenna disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 8-321708 is known. Furthermore, as a conventional small-sized communication device, a portable communication device having a loop antenna disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 4-211198 is known.
However, the communication device disclosed in Japanese Patent Application Laid-Open No. Hei 8-321708 has a built-in coil antenna. As compared with a device having a built-in loop antenna, therefore, it has a problem of a poor receiving sensitivity and degraded communication device performance.
On the other hand, the communication device disclosed in Japanese Patent Application Laid-Open No. Hei 4-211198 has such a structure that a strap for wearing the communication device has a built-in loop antenna. When the communication device is not worn, therefore, the antenna does not take the shape of a loop, and consequently the receiving sensitivity is degraded as compared with that obtained when the communication device is worn. Thus, there is a problem that stable communication performance cannot be always ensured.
In addition, since the strap for wearing has a built-in loop antenna, the thickness of the strap becomes greater accordingly. This results in a problem that the feeling of wearing the communication device is bad and the size of the communication device as a whole becomes large.
Therefore, an object of the present invention is to provide a wristwatch-type communication device capable of enhancing its performance as a communication device, providing favorable feeling of wearing the communication device, and reducing the size of the communication device as a whole.
Another object of the present invention is to provide an antenna suitable for use in the wristwatch-type communication device of the present invention.